1. Field of the Invention
The present invention relates to a technique for calculating, based on measured values measured at a plurality of positions, a desired value (for example, an average value, a maximum value, and a minimum value). The present invention particularly relates to a measurement apparatus and a calculation method that are for calculating such a desired value. Furthermore, the present invention relates to a malfunction detection apparatus and a malfunction detection method that use such a measurement apparatus.
2. Description of Related Art
In solar power plants and wind power plants, several dozens to hundreds of inverter apparatuses are connected to an electric power system in parallel. FIG. 23 is a diagram illustrating a conventional solar power plant. As shown in the drawing, a plurality of inverter apparatuses are connected to an electric power system 101. Each inverter apparatus includes a measurement apparatus 100 and an inverter circuit 102. Measured Values obtained by the measurement apparatuses 100 are input into a monitoring apparatus 103. The monitoring apparatus 103 monitors the operational states of the inverter apparatuses (see, for example, Patent Document 1 below).
Examples of the measured values that are input into the monitoring apparatus 103 include output active powers, output reactive powers, output voltages, and output currents of the inverter circuits 102. Furthermore, other examples include input powers, input voltages, and input currents that are input into the inverter circuits 102 from solar cells, an amount of solar radiation on the solar cells, and temperatures of the solar cells. In FIG. 23, the measurement apparatuses 100 are arranged on the output side of the inverter circuits 102, and are configured to measure an output active power. The monitoring apparatus 103 can calculate the maximum value or minimum value of measured values input from the measurement apparatuses 100, or calculate the average value of these measured values.
Ordinarily, in solar power plants, a large number of inverter apparatuses are installed in a scattered manner in a broad ground. The measurement apparatus provided in each inverter apparatus can be used to recognize a measured value in this inverter apparatus, but cannot be used to recognize measured values in other inverter apparatuses. Therefore, it is not possible to recognize, using the measurement apparatus of one inverter apparatus, the average value of all measured values or the maximum value or minimum value of the measured values.